Production of methyl esters from fatty acids based feedstock as starting materials have been proposed as an alternative raw material for the production of methyl esters. One source of cheaper starting material is vegetable oil fatty acid distillate (FAD) e.g. palm fatty acid distillate (PFAD), soybean fatty acid distillate (SFAD) and others which is a by-product produced from edible palm oil refinery using physical refining process. Other sources of inexpensive starting materials with high FFA content include used frying oil, crops oil, sludge oil and waste oil.
FAD is traditionally used in the production of soap product, sources of feed fat, antioxidant supplement and in the animal feed industry. FAD has also been used as feedstock to recover tocopherols and tocotrienols (vitamin E). There is a promising potential production of monoglyceride using FAD. Typically, FAD contains 70-90% FFA, 10%-25% of neutral lipid and remaining 1-2% of unsaponifiable substances. Direct transesterification of such raw material with FFA more than 3% will result in high soap formation and interfere the subsequent purification of reaction mixture. The excess soap produced will inhibit the separation of the glycerol from methyl ester due to emulsion formation and resulted in low production yield.
Conventionally, esterification process is applied to feed materials with FFA higher than 3% e.g. crude palm oil and PFAD by converting the FFA into methyl ester in the presence of strong acid catalyst and alcohol prior to transesterification reaction. The strong acid catalyst such as sulphuric acid has been widely used in the esterification process. The drawback of using strong acid catalyst is the difficulties of handling and operation due to the high corrosivity of strong acid. This invention relates to the use of mild catalyst for the esterification of vegetable oil with fatty acid more than 3% e.g. bleached and/or degummed palm oil and PFAD prior to transesterification.
U.S. Pat. No. 6,965,044 discloses the esterification of acid oils or acid fats with sulphuric acid with small amount of methanol. Meanwhile, EP 0334154 discloses that the fatty acids are esterified with sulphuric acid, toluene sulphonic acid, chlorosulfonic acid and methylsulphonic acids in alcohol.
Further methods for esterification of free fatty acids are described by using different type of solid catalyst such as ion exchange resin (U.S. Pat. No. 7,256,301, EP 20070254389 and EP 1921131), strong acidic cation exchange resin followed by strong basic anion exchange resin (US 2006/0293533). US 2008/0051599 discloses an acid refined oil which is used as starting material in esterification using citric acid in alcohol.